Our Research

Semiconductors are ubiquitous in electrical and optical applications. It is crucial to understand their structure and dynamics. Existing ultrafast techniques often probe the valence to conduction band transitions, which are delocalized among many atoms. Many charge states, such as trapped charges and polarons, are localized and it is necessary to identify their chemical environments, to further engineering the materials to promote and inhibit these processes. We developed a compact Transient Extreme Ultraviolet (EUV) absorption spectrometer, based on high harmonic generation signals, to study the dynamics of semiconductors. Since the EUV energy triggers the core level transition, it is local and can provide element specific dynamics. With this new technique, we will be able to measure the electron and hole dynamics in semiconductors separately. In a recent study, we found that transient EUV is also sensitive to the nonresonant constant of imaginary refractive index, which reflects the photoemission cryosection, and thereby how deep charges are trapped at surfaces.